Multifunctional konjac glucomannan/xanthan gum self-healing coating for bananas preservation.

Damage to the integrity of the preservation coating on the fruit surface will seriously affect the shelf life of the fruit. In this work, the strong hydrogen bond interaction between xanthan gum (XG) and konjac glucomannan (KGM) could form hydrogel films with self-healing properties. The introduction of gallic acid (GA) was beneficial to further improve the antioxidant activity and UV shielding performance of the composite films. Surprisingly, the mechanical properties and gas (water vapor, O2 and CO2) barrier properties of the KGM film crosslinked by XG were significantly improved. The experiment of banana preservation showed that the composite coating could effectively delay the water loss and browning of bananas, slow down the decomposition of pectin and starch in the flesh, and extend the shelf life of bananas for >6 days. Therefore, this multifunctional coating is an excellent packaging material and has a very broad application prospect in the field of food preservation.

Konjac glucomannan films incorporated pectin-stabilized Mandarin oil emulsions: Structure, properties, and application in fruit preservation.

To enhance the water-resistance and antibacterial properties of KGM films, mandarin oil (MO), was directly emulsified by pectin and then dispersed to the KGM matrix. The effect of MO concentration (0, 0.5, 1.0, 1.5, and 2 wt%) on the performance of the film-forming emulsions as well as the emulsion films was investigated. The results revealed that pectin could encapsulate and protect MO, and KGM as film matrix could further contributed to the high stability of the film-forming emulsions. The FT-IR, XRD, and SEM suggested that MO stabilized by pectin was uniformly distributed in the KGM matrix. The compatibility and good interaction between KGM and pectin contributed to highly dense and compact structure. Furthermore, increasing the concentration of MO effectively improved water-resistance, oxygen barrier, and antimicrobial activity of the KGM based films. The 1.5 wt% MO loaded KGM film had the highest tensile strength (72.22 MPa) and water contact angle (θ = 95.73°), reduced the WVP and oxygen permeability by about 25.8 % and 32.8 times, respectively, prolonged the shelf life of strawberries for 8 days. As demonstrated, the 1.5 wt% MO-loaded KGM film has considerable potential for high-performance natural biodegradable active films to ensure food safety and reduce environmental impacts.

Konjac glucomannan-based nanocomposite spray coating with antimicrobial, gas barrier, UV blocking, and antioxidation for bananas preservation.

Fruit is prone to rot and deterioration due to oxidative browning and microbial infection during storage, which can cause serious economic losses and food safety problems. It is urgent to develop a multifunctional composite coating to extend the shelf life of fruits. In this work, multifunctional quaternized chitosan nanoparticles (QCs/TA NPs) with excellent antibacterial and antioxidant properties were prepared based on electrostatic interaction using tannic acid instead of conventional cross-linking agents. Meanwhile, konjac glucomannan (KGM) with high viscosity, edible and biodegradable properties was used as a dispersant to disperse and stabilize the nanoparticles, and as a film-forming agent to form a multifunctional composite coating. The composite coating exhibited excellent oxygen and water vapor barrier properties, antioxidant, antibacterial, mechanical properties, hydrophobicity, and UV shielding properties. Surprisingly, the oxygen permeability of the K-NPs-15 composite film was as low as 1.93 × 10-13 (cm3·cm)/(cm2·s·Pa). The banana spray preservation experiments proved that the K-NPs-15 composite coating could effectively prolong the shelf life of bananas. Therefore, this study provides a new idea for designing multifunctional freshness preservation coatings, which has a broad application prospect.

Soft and flexible polyvinyl alcohol/pullulan aerogels with fast and high water absorption capacity for facial mask substrates.

Facial mask substrates commonly used in skincare are often considered unhealthy and environmentally unfriendly due to their composition of premoistened nonwovens containing various preservatives. This study aims to address this issue by developing a preservative-free degradable aerogel made from polyvinyl alcohol (PVA)/pullulan (PUL) using a unidirectional freeze-drying method. The aerogels had ordered three-dimensional porous structures and exhibited desirable mechanical properties. They were soft and flexible in both dry and wet states, and their Young's moduli were comparable to that of human skin. The aerogels had high porosity, ranging from 93.0 % to 95.1 %, and exhibited a high water absorption rate and water absorption capacity (ranging from 7.5 g/g to 10.1 g/g). After 30 min of water evaporation, the aerogels showed excellent moisture retention, ranging from 88 % to 93 %. Additionally, the PVA/PUL aerogel efficiently loaded and released active ingredients, such as rapidly releasing ascorbic acid (> 90 % within 30 min). These findings suggest that the PVA/PUL aerogel has potential as a material for facial mask substrates.

Moisture loss inhibition with biopolymer films for preservation of fruits and vegetables: A review.

In cold storage, fruits and vegetables still keep a low respiratory rate. Although cold storage is beneficial to maintain the quality of some fruits and vegetables, several factors (temperature and humidity fluctuations, heat inflow, air velocity, light, etc.) will accelerate moisture loss. Biopolymer films have attracted great attention for fruits and vegetables preservation because of their biodegradable and barrier properties. However, there is still a certain amount of water transfer occurring between storage environment/biopolymer films/fruits and vegetables (EFF). The effect of biopolymer films to inhibit moisture loss of fruits and vegetables and the water transfer mechanism in EFF system need to be studied systematically. Therefore, the moisture loss of fruits and vegetables, crucial properties, major components, fabrication methods, and formation mechanisms of biopolymer films were reviewed. Further, this study highlights the EFF system, responses of fruits and vegetables, and water transfer in EFF. This work aims to clarify the characteristics of EFF members, their influence on each other, and water transfer, which is conducive to improving the preservation efficiency of fruits and vegetables purposefully in future studies. In addition, the prospects of studies in EFF systems are shown.

Towards superior biopolymer gels by enabling interpenetrating network structures: A review on types, applications, and gelation strategies.

Gels derived from single networks of natural polymers (biopolymers) typically exhibit limited physical properties and thus have seen constrained applications in areas like food and medicine. In contrast, gels founded on a synergy of multiple biopolymers, specifically polysaccharides and proteins, with intricate interpenetrating polymer network (IPN) structures, represent a promising avenue for the creation of novel gel materials with significantly enhanced properties and combined advantages. This review begins with the scrutiny of newly devised IPN gels formed through a medley of polysaccharides and/or proteins, alongside an introduction of their practical applications in the realm of food, medicine, and environmentally friendly solutions. Finally, based on the fact that the IPN gelation process and mechanism are driven by different inducing factors entwined with a diverse amalgamation of polysaccharides and proteins, our survey underscores the potency of physical, chemical, and enzymatic triggers in orchestrating the construction of crosslinked networks within these biomacromolecules. In these mixed systems, each specific inducer aligns with distinct polysaccharides and proteins, culminating in the generation of semi-IPN or fully-IPN gels through the intricate interpenetration between single networks and polymer chains or between two networks, respectively. The resultant IPN gels stand as paragons of excellence, characterized by their homogeneity, dense network structures, superior textural properties (e.g., hardness, elasticity, adhesion, cohesion, and chewability), outstanding water-holding capacity, and heightened thermal stability, along with guaranteed biosafety (e.g., nontoxicity and biocompatibility) and biodegradability. Therefore, a judicious selection of polymer combinations allows for the development of IPN gels with customized functional properties, adept at meeting precise application requirements.

Konjac glucomannan-based aerogels with excellent thermal stability and flame retardancy for thermal insulation application.

Biomass aerogels are a promising kind of environment-friendly thermal insulation material. However, the flammability, poor water resistance, and thermal instability of biomass aerogels limit their applications. Herein, freeze-drying and thermal imidization were used to create konjac glucomannan (KGM), boron nitride (BN), and polyimide (PI)-based aerogels with a semi-interpenetrating network structure. The introduction of BN was beneficial to improve the mechanical properties and thermal stability of aerogels. The imidization process of PI improved the hydrophobicity, mechanical property, and flame retardancy of the aerogels. The synergistic effect of PI and BN reduced the peak heat release rate and total heat release rate of KGM-based aerogel by 55.8 % and 35 %, respectively, and endowed aerogel with good self-extinguishing performance. Moreover, the results of thermal conductivity and infrared thermal imaging demonstrated that the aerogels had excellent thermal insulation properties, and could effectively manage thermal energy over a wide range of temperatures. This study provides a simple method for the preparation of heat-insulating aerogel with high fire safety, which has broad application prospects in the field of energy saving and emission reduction.

Properties of konjac glucomannan/curdlan-based emulsion films incorporating camellia oil and the preservation effect as coatings on 'Kyoho' grapes.

The strategy of emulsion coating was used for grape preservation. Camellia oil (CO) was incorporated with KGM/curdlan (KC) to fabricate KC-CO emulsion systems. KC-CO emulsions were analyzed by droplet size distribution and confocal laser scanning microscopy (CLSM), and KC-CO films were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), mechanical properties, dissolution, gas permeability, water contact angle (WCA). KC-CO coating was used for preservation of 'Kyoho' grapes. The results indicated that the addition of CO had a positive effect on KC system. CO could form a uniform emulsion with KC, and the droplets were evenly dispersed in the KC matrix. KC-CO films displayed a continuous microstructure, and elongation at break (EAB) was improved, while tensile strength decreased. The dissolution, water vapor permeability (WVP), and WCA were significantly enhanced, while the permeability of oxygen and carbon dioxide exhibited no advantage compared with KC film. KC-CO-10 possessed optimal properties and was selected as an emulsion coating for preservation. The results suggested that KC-CO-10 significantly maintained the appearance, total solid and acid content of 'Kyoho' grapes, and delayed the weight loss and firmness decrease. This study contributed to the understanding of polysaccharide-lipid emulsion system and the applications.

Legume protein/polysaccharide food hydrogels: Preparation methods, improvement strategies and applications.

For the development of innovative foods and nutritional fortification, research into food gel is essential. As two types of rich natural gel material, both legume proteins and polysaccharides have high nutritional value and excellent application potential, attracting wide attention worldwide. Research has focused on combining legume proteins with polysaccharides to form hybrid hydrogels as their combinations show improved texture and water retention compared to single legume protein or single polysaccharide gels, and these properties can be tailored for specific applications. This article reviews hydrogels of common legume proteins and discusses heat induction, pH induction, salt ion induction, and enzyme-induced assembly of legume protein/polysaccharide mixtures. The applications of these hydrogels in fat replacement, satiety enhancement, and delivery of bioactive ingredients are discussed. Challenges for future work are also highlighted.

Investigation and Characterization of Pickering Emulsion Stabilized by Alkali-Treated Zein (AZ)/Sodium Alginate (SA) Composite Particles.

Pickering emulsions stabilized by food-grade colloidal particles have attracted increasing attention in recent years due to their "surfactant-free" nature. In this study, the alkali-treated zein (AZ) was prepared via restricted alkali deamidation and then combined with sodium alginate (SA) in different ratios to obtain AZ/SA composite particles (ZS), which were used to stabilize Pickering emulsion. The degree of deamidation (DD) and degree of hydrolysis (DH) of AZ were 12.74% and 6.58% respectively, indicating the deamidation occurred mainly in glutamine on the side chain of the protein. After the treatment with alkali, AZ particle size decreased significantly. Moreover, the particle size of ZS with different ratios was all less than 80 nm. when the AZ/SA ratio was 2:1(Z2S1) and 3:1(Z3S1), the three-phase contact angle (θo/w) were close to 90°, which was favorable for stabilizing the Pickering emulsion. Furthermore, at a high oil phase fraction (75%), Z3S1-stabilized Pickering emulsions showed the best long-term storage stability within 60 days. Confocal laser scanning microscope (CLSM) observations showed that the water-oil interface was wrapped by a dense layer of Z3S1 particles with non-agglomeration between independent oil droplets. At constant particle concentration, the apparent viscosity of the Pickering emulsions stabilized by Z3S1 gradually decreased with increasing oil phase fraction, and the oil-droplet size and the Turbiscan stability index (TSI) also gradually decreased, exhibiting solid-like behavior. This study provides new ideas for the fabrication of food-grade Pickering emulsions and will extend the future applications of zein-based Pickering emulsions as bioactive ingredient delivery systems.

Formation and characterization of konjac glucomannan/ethyl cellulose films by using ethanol and water as the solvents.

Hydrophilic konjac glucomannan (KGM)/hydrophobic ethyl cellulose (EC) film was prepared in the ethanol/water environment. The film-forming solution and film properties were both characterized to analyze the molecular interaction changes. Although higher ethanol usage enhanced the stability of the film-forming solution, it did not benefit the film property improvement. The SEM images showed some fibrous structure on the air surface of the films, consistent with the XRD results. The changing trend of mechanical properties and the FTIR results suggested that both ethanol content and ethanol evaporation impacted the molecular interaction during the film formation. The surface hydrophobicity results indicated that the ethanol content could cause significant EC aggregation changes on the film surface only with high EC contents. The water vapor permeability results suggested that higher ethanol usage decreased the compactness of the films. Considering all results, the 20 % ethanol content and the weight ratio of KGM: EC = 7:3 were suggested for the film preparation due to the superior properties in most properties. This study contributed to the understanding of polysaccharide interaction in the ethanol/water environment and offered an alternative biodegradable packaging film.

Study on the Influence of the Preparation Method of Konjac Glucomannan-Silica Aerogels on the Microstructure, Thermal Insulation, and Flame-Retardant Properties.

Natural polysaccharides with high viscosity, good thermal stability, and biocompatibility can improve the mechanical properties of inorganic silica aerogels and enhance their application safety. However, the effects of the preparation methods of polysaccharide-silica aerogels on their microstructure and application properties have not been systematically studied. To better investigate the effect of the microstructure on the properties of aerogel materials, two aerogels with different structures were prepared using Konjac glucomannan (KGM) and tetraethoxysilane (TEOS) via physical blending (KTB) and co-precursor methods (KTC), respectively. The structural differences between the KTB and KTC aerogels were characterized, and the thermal insulation and fire-retardant properties were further investigated. The compressive strength of the KTC aerogels with a cross-linked interpenetrating network (IPN) structure was three times higher than that of the KTB aerogels, while their thermal conductivity was 1/3 of that of the KTB aerogels. The maximum limiting oxygen index (LOI) of the KTC aerogels was 1.4 times, the low peak heat release rate (PHRR) was reduced by 61.45%, and the lowest total heat release (THR) was reduced by 41.35% compared with the KTB aerogels. The results showed that the KTC aerogels with the IPN have better mechanical properties, thermal insulation, and fire-retardant properties than the simple physically blending KTB aerogels. This may be due to the stronger hydrogen-bonding interactions between KGM and silica molecules in the KTC aerogels under the unique forcing effect of the IPN, thus enhancing their structural stability and achieving complementary properties. This work will provide new ideas for the microstructure design of aerogels and the research of new thermal insulation and fire-retardant aerogels.

Characterizations of konjac glucomannan/curdlan edible coatings and the preservation effect on cherry tomatoes.

In this study, konjac glucomannan (KGM) and curdlan were used to fabricate composite coating (KC). The coating solutions were investigated using a rheological method, and the coatings were characterized by water solubility tests, water vapor permeability (WVP), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The preservation effect of KC coating on cherry tomatoes stored at room temperature was determined. Results indicated that the curdlan addition can adjust the hydrophilicity/hydrophobicity of KGM coatings. Curdlan addition enhanced intermolecular entanglement and film-forming property. Increasing curdlan content in KC coatings significantly decreased the moisture content, dissolution and swelling ratio, and WVP. The KGM-curdlan composites behaved as high-performance coatings with good compatibility and uniformity. The K3C2 coating showed the best uniformity, water barrier, and thermal stability. The application of K3C2 coating significantly reduced the weight loss, decay loss, and delayed the decreases of firmness, soluble solids, total acid, and VC contents of cherry tomatoes. The KGM/curdlan edible coatings have promising potential for prolonging the shelf life of cherry tomatoes and applications in fruits preservation in the future.

Increasing agar content improves the sol-gel and mechanical features of starch/agar binary system.

Starch/agar systems are highly potential for versatile applications such as packaging and biomedical materials. Here, how combined factors affect the features of a starch/agar binary system were explored. An increase of starch amylose/amylopectin ratio from 0/100 to 50/50 increased the sol-gel transition temperature and gel hardness of the aqueous starch/agar mixture. An increased agar content (mainly from 30% to 70%) allowed increases in both the tensile strength (reaching 50-60 MPa) and elongation at break of the starch/agar binary films. This phenomenon should be related to the strengthened crystalline structure and the weakened hydrogen bonding between starch chains (reflected by infrared spectroscopy). Furthermore, a higher relative humidity (from 30% to 70%) allowed enhanced chain interactions and probably nanoscale molecular order but weakened the crystalline structure, leading to reduced tensile strength and increased elongation at break. This work could facilitate the design of starch/agar binary systems with improved sol-gel and mechanical performance.

Deacetylation enhances the properties of konjac glucomannan/agar composites.

From a microstructural point of view, this work concerns how deacetylation improves the practical characteristics of deacetylated-konjac glucomannan/agar (DK/A) composite films. As disclosed by infrared spectroscopy and X-ray diffraction, the deacetylation of konjac glucomannan (KGM) enhanced the chain interactions in DK/A composites and suppressed the realignment of agar molecules into crystallites. The enhanced associations between acetyl-free regions of KGM and agar reduced the exposure of OH groups and thus increased the hydrophobicity of the composites. Besides, the partial removal of acetyl groups allowed shortened distances between chains; consequently, denser composite matrices emerged with lower water vapor permeability and higher tensile strength. Also, the KGM deacetylation increased the matrix flexibility and elongation at break for DK/A composites, associated with the hindered rearrangement of agar chains. Thus, altering the deacetylation degree of KGM may be an effective way to design KGM-based composites with improved hydrophobicity and mechanical performance.

Polyvinyl alcohol inclusion can optimize the sol-gel, mechanical and hydrophobic features of agar/konjac glucomannan system.

The practical features (e.g., sol-gel, mechanical and hydrophobic) of biopolymer systems are crucial for their materials applications. This work reveals how polyvinyl alcohol (PVA) inclusion affects the practical features of agar/konjac glucomannan (KGM) system. From rheological analysis, incorporating PVA (especially 6%) enhanced the chain entanglements of resulted ternary solution (A70K24P6) with stabilized sol-gel transition point. Such effect not only increased the zero-shear viscosity (ca. 1.5 times that of agar/KGM counterpart) and structural recovery degree of A70K24P6 solution, but also caused reduced crystallites and simultaneously increased tensile strength, elongation at break and hydrophobicity for A70K24P6 film from solution dehydration. This ternary film exhibited a tensile strength of ca. 105 MPa, an elongation at break of ca. 20%, and a water contact angle of ca. 97.6°. Additionally, incorporating PVA almost unaffected the morphology of film fracture surface. These results are valuable for the design of agar/KGM systems with improved practical features.

Correction: Qiao et al. Microstructure and Mechanical/Hydrophilic Features of Agar-Based Films Incorporated with Konjac Glucomannan. Polymers 2019, 11, 1952.

The authors wish to make the following correction to this paper [...].

Microstructure, Thermal Conductivity, and Flame Retardancy of Konjac Glucomannan Based Aerogels.

With abundant renewable resources and good biodegradability, bio-based aerogels are considered as promising insulating materials for replacing the conventional petroleum-based foam. In this study, konjac glucomannan (KGM)-based aerogels were prepared as thermal insulation materials via a convenient sol-gel and freeze-drying progress with different content of plant polysaccharides, proteins, and wheat straw. The morphology, thermal conductivity, and flame retardancy of KGM-based aerogels were determined. The KGM-based aerogels showed a uniform three-dimensional porous microstructure. The addition of wheat straw could significantly reduce the pore size of aerogels due to its special multi-cavity structure. KGM-based aerogels showed low densities (0.0234-0.0559 g/cm-3), low thermal conductivities (0.04573-0.05127 W/mK), low peak heat release rate (PHRR, 46.7-165.5 W/g), and low total heat release (THR, 5.7-16.2 kJ/g). Compared to the conventional expanded polystyrene (EPS) and polyurethane (PU) foam, the maximum limiting oxygen index (LOI) of KGM-based aerogels increased by 24.09% and 47.59%, the lowest PHRR decreased by 79.37% and 94.26%, and the lowest THR decreased by 76.54% and 89.25%, respectively. The results demonstrated that the KGM-based aerogels had better performance on flame retardancy than PU and EPS, indicating high potential applications as heat insulation in the green advanced engineering field.

Improving konjac glucomannan-based aerogels filtration properties by combining aerogel pieces in series with different pore size distributions.

The pore size distribution of konjac glucomannan (KGM)-based aerogels seriously impacted the air filtration efficiency and filtration resistance. This study aimed to investigate the pore size distribution control of KGM-based aerogels through total solid concentration of the sol and to improve the filtration performance by preparing aerogel stacks, which were made by combining KGM-based aerogels with different pore size distribution (range: 0-180 µm). Results indicated that with increased total solid concentration from 50% to 100% of the origin formulae, aerogel pore size became smaller and the porosity was decreased for all the three sample formulae. Meanwhile, the aerogel mechanical property and filtration efficiency were both strengthened with increased total solid concentration, but the air resistance became significantly higher. The changing extent and rule were influenced by the sample components (KGM, starch, gelatin, wheat straw). The aerogel stacks prepared by in series combining the aerogel pieces with different pore size distribution (from large size to small size) was found to improve filtration efficiency (e.g. from 70% to 80% for K1G2S4WS2) and significantly lower the air resistance (e.g. from 270 Pa to 190 Pa for K1G2S4WS2). This study could guide the filtration performance improvement of aerogels.

Impact of heating and drying temperatures on the properties of konjac glucomannan/curdlan blend films.

The impact of preparation conditions including heating temperature (from 60 °C to 90 °C) and drying temperatures (from 25 °C to 90 °C) on the properties of pure curdlan film and konjac glucomannan (KGM) and curdlan blend films were analyzed. Microstructure analysis indicated the KGM addition could significantly improve the relatively poor film-forming property of curdlan. FTIR and X-ray analysis showed that at high heating temperature 90 °C, molecular interaction might be enhanced in the films due to the stretched structure of curdlan and dissociation of curdlan bundles or triple-helix structure. This was supported by the changes in the mechanical property, surface hydrophobicity, moisture barrier, and moisture tolerance property. The impacts of drying temperature were some different for the curdlan film and KGM/curdlan blend film, and were explained from the molecular hydrophilicity-hydrophobicity, compactness of the films, curdlan conformation, and molecular interaction. This work guided biodegradable film production especially with curdlan added.